Genomic imprinting is the process by which specific genes are marked during gametogenesis to differentially express the two parental alleles. Prader- Willi (PWS) and Angelman (AS) syndromes are distinct neurobehavioral disorders caused by lack of. expression of paternally and maternally inherited genes, respectively from chromosome 15q11-13. Overlapping microdeletions in PWS and AS patients appear to define an imprinting center (IC) that controls resetting of the imprint throughout 15q11-13. The long term goal of this project is to determine the molecular basis of genomic imprinting. For this proposal, the cis- and trans- regulatory elements within the IC and regulatory regions of two imprinted genes, SNRPN and ZNF127 will be characterized. The specific aims of this proposal are to: 1) Iocalize regions of open chromatin by DNasel hypersensitivity mapping; 2) define cis-elements in the hypersensitive region by electrophoretic mobility shift assay (EMSA), and by in vitro and in vivo footprinting; 3) identify trans-factors binding to the elements by EMSA cross-competition, co-migration, or antibody supershifting; 4) clone novel proteins by screening cDNA libraries. Understanding the molecular basis of imprinting may lead to therapeutic approaches for imprinted genetic disorders and pediatric cancers.